Field of the Invention
The present invention relates to a display device and a method of manufacturing the same and, more particularly, to a display device including a light shielding material.
Discussion of the Related Art
Recently, flat panel displays (FPD) have become more important with the development of multimedia. In line with such a trend, a variety of types of displays, such as liquid crystal displays (LCDs), plasma display panels (PDPs), field emission displays (FEDs), and organic electroluminescent displays (OLEDs), are being commercialized. OLEDs have high response speed of 1 ms or less and low power consumption, and are a self-light emission type. Because of these advantageous characteristics, OLEDs have been in the spotlight as a next-generation display device, especially due to their excellent viewing angle.
A method of driving a display device includes a passive matrix method and an active matrix method that uses a thin film transistor. In the passive matrix method, a positive electrode and a negative electrode are formed to cross each other, and a line is selected and driven. In the active matrix method, a thin film transistor is connected to each pixel electrode and driven in response to a voltage maintained by a capacitor connected to the gate electrode of the thin film transistor.
In addition to the basic characteristics of thin film transistors, such as mobility and leakage current, durability relating to a long lifespan and electrical reliability of thin film transistors are also important. The active layer of a thin film transistor used for display devices has been commonly made of amorphous silicon or polysilicon. Amorphous silicon is advantageous in that a film formation process is simple and manufacture costs are low, but electrical reliability may not be secured. On the other hand, polysilicon also has a problem in that its application to a large-sized device may be difficult due to its high temperature process and non-uniformity in crystallization.
If the active layer is made of oxide, a high mobility can be obtained at a low temperature, and it is easy to obtain desired properties because its resistance can be controlled depending on the content of oxygen. Accordingly, oxide has been recently attracting great attraction as a material for the active layer of a thin film transistor. Examples of oxide materials in use are zinc oxide (ZnO), indium zinc oxide (InZnO), or indium gallium zinc oxide (InGaZnO4).
A thin film transistor including an oxide active layer beneficially has a light shielding layer for protecting the active layer against external light. This is because the active layer may become unstable if a photocurrent is generated in the active layer by an external light source.
A conventional light shielding layer may be configured to include a reflection layer. For example, the conventional light shielding layer may include a metal layer and an insulating layer or may include a metal layer having a surface brought in contact with an oxide active layer. The conventional light shielding layer may further include an insulating layer for absorbing light, and may be, for example, made of amorphous silicon or silicon carbide (SiC).
However, the aforementioned materials as a material for the active layer of a thin film transistor may not satisfy heat-resistant, high resistance, low reflection and low transmittance characteristics. In particular, amorphous silicon has high reflectance of about 30%, a multi-layer including SiNx has high reflectance of about 14%, and black-series silicon carbide has high reflectance of about 11 to 25%. Accordingly, reliability of a display device may deteriorate due to deterioration of the active layer of a thin film transistor attributable to the light introduced into the active layer from the backlight of an LCD or outside of an OLED.